1 L. J. Yuan et al. / Journal of Water Sustainability 3 (2011) 1-10
* Corresponding to: [email protected]
Modified Operation in SBR Applied to Decentralized Domestic
Sewage Treatment for High Quality Effluent
Lin Jiang Yuan1*
, Jie Zhao1, Kai Yang
1, Zhi Ying Wang
1
1School of Environmental and Municipal Engineering, Xi’an University of Architecture and Technology, Xi’an,
710055, China
ABSTRACT
SBR can be used as the sole reactor for SS, COD, and nutrient removal and is suitable for decentralized wastewater
treatment, but it is noticed that the SBR is difficult to obtain high quality effluent meeting up to Grade 1A standard
in China in many practical cases. In this study sewage from a university campus was used as decentralized sewage,
and its treatment of SBR was investigated. Two operating modes were adopted to study whether SBR can serve as
sewage treatment with high quality effluent that may meet the standard of water reuse to some extent. The results
show that, after changing anaerobic and aerobic stage, the SBR can remove as more as 90%, 92%, 67% and 89% of
COD, ammonium nitrogen, total nitrogen and phosphate of the sewage, respectively, and effluent meet water
quality for reuse. Proper alternation of anoxic condition (lasting for 30min before feeding), anaerobic condition
followed (lasting 1h after feeding) and aerobic condition (for 2h with low dissolved oxygen less than 2mg/l all the
way) is the foundation for effluent of good quality and stable operation. The results suggest that the SBR performed
very well to treat sewage of low carbon to nitrogen ration and large fluctuation in water quality, and it is suitable for
decentralized wastewater treatment and water reclamation. Operation control of the SBR can not only save energy,
but also can dispense with advanced water treatment of water reclamation to some extent.
Keywords: Decentralized wastewater treatment; SBR; Water reclamation; Biological nutrient removal
1 INTRODUCTION
With increasing attention on water pollution
control in China, treatment of wastewater
discharged from area out of service of urban
centralized drainage system, i.e. decentralized
wastewater, becomes more and more urgent.
Decentralized wastewater has some distin-
guished differences from common municipal
wastewater. For example, it is small in quan-
tity in most cases. The quantity maybe varies
from several cubic meters to hundreds. The
figure may be thousands in some residential
areas and towns and villages. Secondly, there
is large fluctuation in both wastewater quanti-
ty and quality (Bian and Yuan, 2009). Due to
obvious relevancy and high consistent with
work and rest of residual in water used and
discharge, both wastewater quantity and
quality vary greatly with time throughout the
day. Sometimes they are intermittent. There
hardly has sewage discharged by community
in midnight and from university campus in
vacation. Finally, the strength of decentralized
wastewater is usually lower compared with
municipal wastewater, especially in carbon to
nitrogen ratio (Ma et al., 2009).
In many cases of decentralized wastewater
treatment, there are lack of professional
Journal of Water Sustainability, Volume 1, Issue 3, December 2011, 259-268
© University of Technology Sydney & Xi’an University of Architecture and Technology
260 L. J. Yuan et al. / Journal of Water Sustainability 3 (2011) 259-268
operator and manager who are absolutely
necessary in big municipal wastewater treat-
ment plant. Complicated treatment process,
high capital cost and operation cost may not
be acceptable in addition. Under these cir-
cumstances, treatment of low cost and simple
process is welcome (Massoud et al., 2009).
Many designers are apt to adopt SBR (se-
quencing batch reactor) and its derivative
technologies, such as CASS (cyclic activated
sludge system) in decentralized wastewater
treatment (Ng et al., 1993; Bernardes and
Klapwijk, 1996; Kassaba et al., 2011). Based
on investigation of performances of a few
decentralized wastewater treatment facilities
located in Xi’an city, China, it has been found
that most of their performances are not stable
and their effluents cannot meet discharge
standard required (class 1B of GB 18918
-2002). It is considered that proper operating
strategy is the foundation of satisfying effluent.
How to deal the conflicts among COD,
nitrogen and phosphorus removal in the
unique tank of SBR still needs to study.
If advanced treatment is applied after sec-
ondary treatment of decentralized wastewater
to reclaim water, this process will lose ad-
vantage. In another scenario, if the effluent
from common secondary treatment in the SBR
is of high quality that can be served as recla-
mation water after filtration (if necessary) and
disinfection for landscape water supply and
green sprinkle, it will be appealing in practice.
A SBR was applied in this study to treat the
sewage discharged from a university campus
as decentralized wastewater. Key operation
parameters and mode for secondary treatment
for high quality effluent was studied in order
to find out a solution for decentralized
wastewater treatment and reuse.
2 MATERIALS AND METHODS
2.1 Experiment Setup
The experiment setup is illustrated in Figure 1.
Reactor was a plexiglas tank with 250-liter
effective working volume. Size of the tank is
92 ×60 ×55 cm (L×B×H) and water depth is
less than 50 cm. 4 perforated tubes fixed on
the bottom of the tank were applied as oxygen
diffuser. Air supply rate was controlled via air
flow meter. 2 stirrers were applied to mix liq-
uid in the tank when there was no aeration.
2.2 Wastewater and Inoculation Sludge
Raw sewage from drainage of campus of a
university in Xi’an city was applied. Water
quality of the sewage is shown in Table 1.
Activated sludge from A2O system of Deng
Jia Cun municipal wastewater treatment plant
was inoculated, and its concentration in the
reactor was about 2200 mg/L (MLVSS) with
SVI of 180 L/g.
2.3 Operating Procedures of the System
Reactor was operated 4 cycles (6 h per cycle)
per day. Two operating modes were adopted,
namely Run 1 and Run 2. The system was
operated under Run 1 for 60 days and Run 2
for 120 days. Operating procedure of Run 1
was as follows: feeding with stirring for 0.5 h-
anaerobic mixing for 1h- aeration for 2 h-
anoxic mixing for 1h- aeration for 0.5 h-
precipitation for 55 min- drawing for 5 min
(i.e. Ana-O-Ano-O mode).
Table 1 Quality of the sewage
item CODcr SS PO43-
-P NH4-N TP TN
Conc. (mg/L) 132~320 122~455 1.2~6.9 15~35 1.5~7.8 35~60
L. J. Yuan et al. / Journal of Water Sustainability 3 (2011) 259-268 261
1
2
3
4
5
6 8
4 4
7
5
7 7
9
Figure 1 Schematic diagram of the experiment system (1. drainage pipeline; 2.feeding pump;
3. processor; 4. air pump; 5. mixer; 6. SBR reactor; 7. perforated tube; 8. drawing
pump; 9. DO meter)
In Run 2, operating procedure was mixing for
0.5 h before feeding, and then feeding with
stirring for 0.5 h. Anaerobic mixing for 1h-
aeration for 2h- precipitation for 1h- drawing
for 5 min- idle for 55min (i.e. pre-Ano–Ana-
O mode) (Table 2). Temperature in the reactor
was at 27~33˚C during the experiment. SRT
maintained at 15 d. Volume changing ratio
was 50% in one cycle. DO was maintained at
2-4 mg/L in the aerobic phase in Run 1 and
0-1.5 mg/L in Run 2.
2.4 Analysis Methods
The concentrations of COD, ammonium, ni-
trate, total nitrogen, phosphate, and total phos-
phorus were determined following the me-
thods set out in the standard methods (China
EPA, 2002). COD was determined by dichro-
mate method, ammonia by Nessler’s reagent
colorimetric method, nitrates by ultraviolet
spectrophotometric method, total nitrogen by
potassium persulfate digestion- UV Spectro-
photometric method, phosphate by ammonium
molybdate spectrophotometric method, and
total phosphorus by potassium persulfate
digestion- ammonium molybdate spectropho-
tometric method.
3 RESULTS AND DISCUSSION
3.1 Performance of the System Operated
in Run 1
Performance of the system operated in Run 1
is shown in Figure 2. As shown in Figure 2a to
2e, average removal rates of the system for
COD, ammonium nitrogen, phosphate, total
nitrogen and suspended solids are about 90%,
97%, 93%, 67% and 95%, respectively. The
average concentrations of COD, ammonium
nitrogen, phosphate, total nitrogen and sus-
pended solids in effluent are about 32, 0.71,
0.21, 14.63 and 12.45 mg/L, respectively.
Table 2 Operating modes in a cycle of Run 1 and Run 2
Period 0.5h 0.5h 0.5h 0.5h 0.5h 0.5h 0.5h 0.5h 0.5h 0.5h 0.5h 0.5h
Run 1 F & S Ana Oxic Anoxic Oxic P & D
Run 2 S F & S Ana Oxic P D & Idle
Note: F-feed, S-stirring, P-precipitation, D-drawing, Ana-anaerobic.
262 L. J. Yuan et al. / Journal of Water Sustainability 3 (2011) 259-268
0
100
200
300
400
500
600
0 5 10 15 20 25 30 35 40 45 50 55 60
Time (d)
CO
D (
mg/L
)
0
20
40
60
80
100
Rem
oval
rat
e (%
)
inf eff Removal rate
0
1
2
3
4
0 5 10 15 20 25 30 35 40 45 50 55 60
Time (d)
P (
mg
/L)
0
20
40
60
80
100
Rem
ov
al r
ate
(%)
inf eff Removal rate
0
10
20
30
40
0 5 10 15 20 25 30 35 40 45 50 55 60
Time (d)
NH
4-N
(m
g/L
)
0
20
40
60
80
100
Rem
oval
rat
e (%
)
eff inf Removal rate
As a whole, the system performed well on
removing of ammonium, but not very well on
its removal of total nitrogen and phosphate.
Figure 2a
Figure 2b
Figure 2c
L. J. Yuan et al. / Journal of Water Sustainability 3 (2011) 259-268 263
0
10
20
30
40
50
60
0 5 10 15 20 25 30 35 40 45 50 55 60
Time (d)
TN
(m
g/L
)
0
20
40
60
80
100
Rem
oval
rat
e (%
)
inf inf Removal rate
0
100
200
300
400
500
0 5 10 15 20 25 30 35 40 45 50 55 60
Time (d)
SS
(m
g/L
)
0
20
40
60
80
100
Rem
oval
rat
e (%
)
inf eff Removal rate
Figure 2d
Figure 2e
Figure 2 Performance of the system operated in Run 1
CC
OD
0
10
20
30
40
50
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 6
0
100
200
300
400
500
P NH4-N NO3-N TN COD
fill Ana Oxic Anox Draw Oxic
CO
D (
mg
/L)
NH
4-N
, N
O3-N
, T
N,
P (
mg
/L)
Time (h)
Figure 3 The profiles of ammonium phosphorus, nitrate, total nitrogen and COD in a typical
cycle in Run 1
264 L. J. Yuan et al. / Journal of Water Sustainability 3 (2011) 259-268
0
100
200
300
400
500
600
0 20 40 60 80 100 120Time (d)
CO
D (
mg/L
)
0
20
40
60
80
100
Rem
oval
rat
e (
%)
inf eff Removal rate
0
1
2
3
4
0 20 40 60 80 100 120
Time (d)
P (
mg
/L)
0
20
40
60
80
100
Rem
oval
rat
e (
%)
inf eff Removal rate
Figure 3 shows the profiles of ammonium,
phosphorus, nitrate, total nitrogen and COD
in a typical cycle in Run 1. As shown in the
figure, the lower removal for nitrite and total
nitrogen is considered to be due to scarce of
carbon source in anoxic stage where denitri-
fication occurred.
3.2 Performance of the System Operated
in Run 2
To improve the removal ability of the total
nitrogen and phosphate, operating mode of
the system was changed into mode 2, i.e.,
Run 2. The performance of the system in Run
2 is shown in Figure 4.
As shown in Figure 4a to 4e, average re-
moval rates of the system for COD, ammo-
nium nitrogen, phosphate, total nitrogen and
suspended solids are about 93%, 93%, 96%,
75% and 95%, respectively. The average
concentrations of COD, ammonium nitrogen,
phosphate, total nitrogen and suspended
solids in effluent are about 27.4, 2.1, 0.07,
11.7 and 10.6 mg/L, respectively. The system
performed better on removing of total nitro-
gen and phosphate ammonium compared with
that of Run 1. What is more attractive, Run 2
has a lower energy cost in aeration due to
control lower concentration in aerobic stage
and shorter aeration period. But That it
resulted in a little higher concentration of
ammonium in effluent of Run 2 of about 2.1
mg/L (average) should be noticed.
Figure 4a
Figure 4b
L. J. Yuan et al. / Journal of Water Sustainability 3 (2011) 259-268 265
0
10
20
30
40
0 20 40 60 80 100 120
Time (d)
NH
4-N
(m
g/L
)
0
20
40
60
80
100
Rem
oval
rat
e (%
)
eff inf Removal rate
0
10
20
30
40
50
60
0 20 40 60 80 100 120
Time (d)
TN
(m
g/L
)
0
20
40
60
80
100
Rem
oval
rat
e (%
)
inf inf Removal rate
0
100
200
300
400
500
0 20 40 60 80 100 120
Time (d)
SS
(m
g/L
)
0
20
40
60
80
100
Rem
ov
al r
ate
(%)
inf eff Removal rate
Figure 4c
Figure 4d
Figure 4e
Figure 4 Performance of the system operated in Run 2
266 L. J. Yuan et al. / Journal of Water Sustainability 3 (2011) 259-268
0
5
10
15
20
25
0 0.5 1 1.5 2 2.5 3 3.5 4 5
Time(h)
NH
4-N、
NO
3-N、
TN、
P(m
g/L
)
0
10
20
30
40
50
CO
D(
mg
/L)
P NH4-N TN NO3-N COD
Feed AnaOxic Drawn
Pre-
anoxic
Figure 5 The profiles of ammonium, phosphorus, nitrate, total nitrogen and COD in a typical
cycle in Run 2
Figure 5 shows the profiles of ammonium,
phosphorus, nitrate, total nitrogen and COD in
a typical cycle in Run 2. As shown in the
figure, because of 30 min of pre-anoxic
stirring before feeding the system, total
nitrogen and nitrate were removed thoroughly
that improved the anaerobic phosphorus
release in anaerobic stage followed.
3.3 Discussion
It is commonly accepted that biological
nitrogen removal conflicts with biological
enhanced phosphorus removal due to compe-
tition for carbon source and different condi-
tion needed (Kuba et al., 1996; Third et al.,
2003; Yuan et al., 2007). High effective
biological nutrient removal in SBR will be
more difficult due to unique tank. In order to
remove nitrogen and phosphate in decentral-
ized domestic sewage, alternating operation
condition is indispensable (Pochana and
Keller, 1999; Zhao et al., 1999).
From the results of this study, it is indicated
that the system could achieve good perfor-
mance on both nitrogen and phosphate re-
moval operated in the two modes. There is
hardly difference between the operations in
Run 1 and Run 2 in removals of COD, SS,
ammonium, total nitrogen and phosphate. It is
suggested that the operating strategies of the
system were proper. In Run 1, the removal of
ammonium is more effective than that of
Run2, but it is reverse for total nitrogen and
phosphate removal. The reason for high
efficient removal of total nitrogen and phos-
phate achieved in Run 2 is considered as that
pre-anoxic stage before feeding greatly
benefited phosphate release of PAOs in
anaerobic stage followed and simultaneously
organic substance oxidization, nitrification,
denitrification with excessive phosphate
uptake in oxic stage whit DO of less than 1.5
mg/L (DO was almost null within the first 30
min, and in the 30 min followed, DO was less
than 1 mg/L, finally it increased to not more
than 1.5 mg/L).
Concentrations of COD, TN, ammonium
nitrogen and phosphate in the effluents in the
two operation modes are less than 50, 15, 5,
and 5 mg/L, respectively. Qualities of the
effluents of the reactor operated under both
modes even met the Standard for Pollutants
Discharged from Municipal Wastewater
Treatment Plant (GB18919-2002) of 1A class,
only SS of 12.45 and 10.63 mg/L in average
in mode1 and 2, respectively, is slightly
higher than the standard limitation of 10 mg/L.
The effluents basically meet reclaimed water
quality applied for miscellaneous usage in
L. J. Yuan et al. / Journal of Water Sustainability 3 (2011) 259-268 267
case of less requirements of SS. Otherwise,
simple coagulation/ filtration applied can
make SS in the effluents meet usage of more
stringent requirements for reclaimed water. It
is suggested that the treatment achieved
wastewater treatment and water reclamation
simultaneously.
From Figures 2 and 4, it can be seen that
the influent of the system fluctuated very
obviously in quality, but the effluent was very
stable. It implies that the treatment of the SBR
has a good capacity for water quality fluctua-
tion, which suitable for decentralized
wastewater treatment. It is found that after
feeding, COD to TN ratio in the reactor is 4:1
to 2:1, that means organic substance in the
influent is not enough for nitrogen and phos-
phate removal (Narkisa, 1979; Chiu and
Chung, 2003). As discussed above, by appli-
cation of DO control strategy in aerobic stage,
simultaneous nitrification and denitrification
as well as denitrifying phosphorus accumula-
tion of PAOs occurred (Figure 5), and as a
result organic substance needed for nitrogen
and phosphate removal was saved. It is
demonstrated proper operation strategy set is
basic for good effluent of the SBR.
CONCLUSIONS
Both Ana-O-Ano-O mode and pre-Ano-Ana
-O mode can achieve effluents of good quality
that may satisfy reuse purpose to some extent.
Mode 2 with lower operation cost and simpler
operation is more appealing for application.
The SBR is adequate to decentralized domes-
tic wastewater treatment with high quality
effluent. Proper operation strategy is basic for
good effluent.
ACKNOWLEDGEMENT
This research was supported by National Key
Science and Technology Projects on Water
Pollution Control and Management (Grant NO.
2009ZX07212-002-004-002, 2009ZX07212-0
02-004-003), National Natural Science Foun-
dation of China (Grant NO. 50878180,
51078304), and EU-China River Basin Man-
agement Program.
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